Originally Posted by vstech

mobil 1 10W40 is not diesel rated.
ya really need to find the 5W40 TD&T from mobil one.
however, even that is no longer a group IV synthetic, so Rotella Blue bottle T6 and all the other synthetics are in the same league for protection on the diesel vehicles.
only Amsoil and a few others are in the TRUE synthetic league now... and they are NOT inexpensive.

Originally Posted by bustedbenz

The owners manual was written back when the standards were a little different... 10W-40 has now fallen out of common use as a diesel-rated oil. The additive packages are different and diesel-rated oils handle the soot load better, which gas engines don't put on it.

The manual is basically saying, if you can find a diesel-rated 10W-40 then that weight/temperature range is acceptable... but oil isn't just about the weight number, it's also about the rating and intended use. Back in the '80s, maybe there were more diesel weights than we use now... pretty much now, dino diesel oil is either 15w-40 (most common by far) or 20W-50, and synthetic is typically 5w-40. Rotella makes a synthetic blend for diesels in 10W-30 and maybe 10W-40 also, but those are pretty much the one exception in a world where it's uncommon.

If you use the gas rated oil this time just to get rid of it, I'd consider changing it after 5,000 miles instead of running a longer interval with it. In spite of being synthetic, since it isn't the "right" synthetic, I'd dump it at 5k if it was me just so I didn't have to wonder.

To a certain extent... oil is oil is oil. If it's slick like oil and turns black like oil and lubricates moving parts like oil -- it's good enough. But, if you're shooting for "ideal" rather than just "acceptable"... I'd say use what you've got for 5k miles and then put diesel oil in next time and things will most likely be just fine.

PLENTY of these things get used for years with gas-rated oil due to Jiffy lube not knowing any better, and presumably they're still moving. If you don't run OUT of oil, chances are, nothing will wear prematurely.

My $0.02. As always, if something goes wrong, I'm not liable.

Originally Posted by Skippy

If you haven't put it in yet, and it satisfies JASO MA, just use it in your motorcycle instead. Don't have a motorcycle? Get one, they're loads of fun.

Yes, it will work in a 300D in a pinch, but I'd much rather use a diesel rated oil. If you check the package and the oil in question IS diesel rated, then it will be fine.